1. Field of the Invention
This invention relates to a method and apparatus for testing the quality of engine coolants and heat-exchange fluids. More particularly, this invention relates to a field test, requiring a minimum of operator interaction.
2. Related Art
Recently Organic Acid Technology (OAT) coolants and heat exchange fluids have been introduced commercially, and provide improved corrosion protection and long life. OAT corrosion inhibitor packages in aqueous and glycol concentrates are used in automotive, heavy duty, marine and industrial applications. OAT inhibitors are also used in secondary cooling systems and in a variety of industrial heat exchange fluids. The use of monocarboxylic or dicarboxylic acids, or the salts of such acids, as corrosion inhibitors in antifreeze/coolant and heat-exchange fluid compositions is disclosed for instance in EP-A-0 479 470, -0 564 721 and -0 573 287. Such compositions may also contain a variety of additives for special purposes, such as hydrocarbyl triazoles for corrosion protection of copper and copper alloys (EP-A-0 564 721).
There is a need to check the quality of the coolant solution regularly to ensure problem-free operation. For the development of OAT coolants, organic acids were neutralized with alkali metal hydroxides (preferably sodium hydroxide (NaOH) or potassium hydroxide (KOH)) to obtain the inhibitor salts used in the new organic formulations, see for example, U.S. Pat. Nos. 4,647,392; 4,851,145; and 4,759,864. It was soon realized that an acid titration of an OAT solution could provide information on the total carboxylic acid inhibitor content. U.S. Pat. No. 5,366,651 shows in FIG. 1 some titration curves for combinations of carboxylate inhibitors with an organic pH buffer such as imidazole.
In order to evaluate the OAT coolant quality in the field, the end user needs to be able to check the amount of contamination with other coolants, as well as carboxylate inhibitor content. The present invention provides an improved method and apparatus for field testing and analysis of coolants and heat exchange fluids.
According to one aspect of the invention, there is provided a test method for determining the content of carboxylic acid-based corrosion inhibitors in a coolant or heat exchange fluid which comprises:
(a) placing a sample comprising a predetermined amount of the material to be tested in a titration vessel,
(b) stirring or otherwise agitating the sample while adding an acidic reagent at a constant rate,
(c) measuring the pH of the stirred sample while the acidic reagent is added,
(d) determining a first equilibrium point (EP1) demonstrated by a first rapid drop in pH,
(e) continuing addition of acidic reagent and measuring the pH until a second equilibrium point (EP2), demonstrated by a second rapid drop in pH, is reached, and
(f) determining the amount of carboxylic acid-based corrosion inhibitor in the sample from the amount of acidic reagent added between EP1 and EP2.
Other aspects of the invention provide:
A method wherein the content of contaminant in the sample is determined from the amount of acidic reagent required to reach the first equilibrium point.
A method wherein the amount of freezing point depressant in the sample is determined from the refractive index of the sample.
A method wherein the pH is determined by means of a calibrated electrode in the titration vessel.
A method wherein at least one quantity selected from the observed values of pH, the amount of carboxylic acid corrosion inhibitor, the amount of contaminant, the refractive index, and the freezing point of the sample is displayed visually.
According to another aspect of the invention, there is provided an apparatus for conducting a test method as described above which comprises a titration vessel, first and second reservoirs for acidic reagent and waste neutralizing agents respectively, a first pump for transferring acidic reagent from the first reservoir to the titration vessel and a second pump for transferring waste neutralizing agent to the titration vessel from the second reservoir, a stirrer for stirring samples in the titration vessel, a pH electrode in the titration vessel, display means for displaying information determined by tests conducted in the apparatus, and electronic control means for controlling said apparatus.
The present invention is directed towards a field- or laboratory test technique to determine the quality of antifreeze/coolant or aqueous heat-transfer or heat-exchange fluids. An apparatus and method are described by means of which it is possible to measure the content of carboxylate corrosion inhibitors in OAT coolants or heat exchange fluids, such as Havoline Extended Life Coolant (XLC) (Havoline products available from Texaco Inc.), or heat exchange fluids containing Havoline Extended Life Corrosion Inhibitor (XLI) or mixtures thereof. In one preferred aspect of the invention, the method is used to also measure the contamination level in XLC contaminated by traditional borate or phosphate containing coolant or with the more recently introduced hybrid OAT-traditional coolants such as Havoline Antifreeze Coolant (AFC). Alternatively, it is of course possible to make calibrations for other OAT coolants.
In another aspect of the present invention, the measurement of contamination level, carboxylate corrosion inhibitor content is combined with a measurement of the pH of the test solution.
In yet another preferred aspect of the invention, the measurements of contamination level, total carboxylate inhibitor content and pH are combined with a refractometric determination of the freezing point of the test solution.